well,as far as to my knowledge,this is a mere superstition related to evil,as according to shakespearen plays cats ,generally black ones are the signs of evil and they have close association with witches..and 9 lives can may be due to the reason that people of ancient times considered that witches would travel across,transforming themselves as cats,and nobody could harm them,even if one tried witches regenerated and no. 9 comes from magical odd number of witches i.e 3